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Thu, 08 Oct 2026 10:05:49 -0700 (PDT) Received: from localhost.localdomain ([117.88.121.66]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-82fc8873349sm131411a34.13.2026.10.08.10.05.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Oct 2026 10:05:49 -0700 (PDT) From: Henry Martin To: Namjae Jeon , Sergey Senozhatsky , Tom Talpey , ChenXiaoSong , Gael Blivet Cc: linux-cifs@vger.kernel.org, linux-kernel@vger.kernel.org, Henry Martin Subject: [PATCH] ksmbd: fix heap out-of-bounds write in SMB2_CREATE context stacking Date: Fri, 9 Oct 2026 01:05:42 +0800 Message-ID: <20261008170542.1034301-1-bsdhenrymartin@gmail.com> X-Mailer: git-send-email 2.43.7 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit smb2_open() appends up to six create contexts (lease, mxac, disk_id, durable, posix, aapl) back-to-back without checking the total length against work->response_sz. A non-compound SMB2_CREATE only gets the 448-byte small response buffer, which also carries the 4-byte rfc1002 length word, leaving 292 bytes for contexts. The AAPL response alone occupies 128 fixed bytes, so a client stacking contexts (up to 416) overruns the kmalloc-512 object into the adjacent allocation with a deterministic zero-fill. Compute the worst-case context total from the per-dialect conn->vals->create_*_size table and grow the response buffer to fit before writing any context, so legitimate requests keep working unchanged. This vulnerability was discovered by Tencent CodeBuddy Security. Fixes: 8f1b796ff1135 ("ksmbd: add AAPL kAAPL_SERVER_QUERY create context support") Signed-off-by: Henry Martin --- fs/smb/server/smb2pdu.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 6b8809f67b926..e18e6b630f757 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -5162,6 +5162,52 @@ int smb2_open(struct ksmbd_work *work) rsp->CreateContextsLength = 0; iov_len = offsetof(struct smb2_create_rsp, Buffer); + /* + * The create contexts below are appended back-to-back with no + * length check, while a non-compound CREATE only gets the 448-byte + * small response buffer; a client stacking lease+mxac+disk_id+ + * durable+posix+AAPL contexts overruns it (the AAPL response alone + * memsets 128 fixed bytes). Compute the worst-case total and grow + * the buffer before writing any context. Note that response_buf + * also carries the 4-byte rfc1002 length word before the SMB2 + * header. + */ + { + size_t ctx_max = 0; + size_t need; + void *nbuf; + + if (opinfo && opinfo->is_lease) + ctx_max += conn->vals->create_lease_size; + if (maximal_access_ctxt) + ctx_max += conn->vals->create_mxac_size; + if (query_disk_id) + ctx_max += conn->vals->create_disk_id_size; + if (durable_rsp && dh_info.type == DURABLE_REQ_V2) + ctx_max += conn->vals->create_durable_v2_size; + else if (durable_rsp && dh_info.type == DURABLE_REQ) + ctx_max += conn->vals->create_durable_size; + if (posix_ctxt) + ctx_max += conn->vals->create_posix_size; + if (aapl_ctxt) + ctx_max += conn->vals->create_aapl_size; + + need = 4 + offsetof(struct smb2_create_rsp, Buffer) + ctx_max; + if (need > work->response_sz) { + nbuf = kvzalloc(need, KSMBD_DEFAULT_GFP); + if (!nbuf) { + rc = -ENOMEM; + goto err_out; + } + memcpy(nbuf, work->response_buf, + 4 + offsetof(struct smb2_create_rsp, Buffer)); + kvfree(work->response_buf); + work->response_buf = nbuf; + work->response_sz = need; + rsp = smb_get_msg(work->response_buf); + } + } + /* If lease is request send lease context response */ if (opinfo && opinfo->is_lease) { struct create_context *lease_ccontext; -- 2.43.7